US5405512A - Gas sensor and method - Google Patents
Gas sensor and method Download PDFInfo
- Publication number
- US5405512A US5405512A US08/264,266 US26426694A US5405512A US 5405512 A US5405512 A US 5405512A US 26426694 A US26426694 A US 26426694A US 5405512 A US5405512 A US 5405512A
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- gas
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/416—Systems
- G01N27/4163—Systems checking the operation of, or calibrating, the measuring apparatus
Definitions
- the present invention is directed to electro-chemical sensors of the type which have consumable electrodes and related electronic circuits, and which can operate on either galvanic or polarographic principles.
- a commonly used prior art system comprises a housing, a cathode (or sensing electrode), one or more consumable anodes (counter-electrodes), electrolyte, and a gas limiting control member such as a gas permeable membrane or gas diffusion membrane or, in some cases, a capillary structure (any of which flow limiters may be used to limit movement of the gas to be sensed to the sensing electrode.)
- the cathode electrode and the anodes are connected in a sensing circuit
- the magnitude of the current flow measured is proportional to the gas being sensed at the cathode (sensing electrode) which may be any of a number of active materials such as gold, silver, platinum, nickel, etc., the selection criteria for which is known to those skilled in the art.
- Electrochemical reduction takes place at the cathode, and the anode (lead or copper, for example, which supplies the electrons to permit the reduction) is consumed.
- dual cathode sensing circuits (FIG. 1b) have been provided with the sensor components in a common housing. While these redundancy-type units serve some purpose, they do not tell the user when the end of anode life is approaching any more accurately than a single cell/circuit unit.
- FIG. 1d It has been suggested (FIG. 1d) that a common cathode/dual anode system with one of the anodes being somewhat smaller than the other anode, and with a detection circuit to measure the current from each anode, could provide a solution to the problem. It is believed that this cannot work as a practical means of detecting remaining anode life since the electrons, at any particular time, may come from either anode in whatever proportion is dictated by uncontrollable phenomena, and this proportion will continually vary with time. In other words, the amount of useable material remaining in the anodes will not determine which anode supplies a preponderance of electrons at any given time during the normal life of the cell.
- the total number of electrons which are being provided by the anode(s) in a properly functioning sensor is determined by the number of gas molecules available to be reduced at the cathode and not by the state of the anode. Otherwise, it would not be a gas sensor.
- the object of the present invention is to provide a solution to the problem of end-of-life anode consumption and sudden sensor failure.
- the present invention takes a new approach to solving the problem.
- a common cathode and sensing circuit are switched or multiplexed back and forth in alternating sequence between two or more anodes.
- the sensing circuit is in addition to measuring the current flow to determine gas concentration, designed to detect a variation in signal as a function of which anode is being used to supply the electrons in the reaction.
- the system then knows that a given anode of the cell is reaching the end of its useful life when it can no longer supply electrons at the same rate as the other anode(s).
- a common anode and sensing circuit is switched or multiplexed between two or more cathodes in similar fashion.
- FIG. 1a, 1b and 1c are examples of prior art gas sensor systems, and FIG. 1d is a block diagram of a suggested solution,
- FIG. 2a is a schematic diagram of the sensor system incorporating the invention.
- FIG. 2b is a schematic block diagram of a further embodiment of the invention.
- FIG. 1a discloses a generic galvanic gas sensor system 10 in which a gas movement or transport control member 11 conveys gas to be sensed to a cathode (sensing electrode) 12, electrolyte 13, and anode 14 which are connected via a load resistor (or resistance network) 15 to sensing circuit 16 which supplies an output signal to a utilization device 17 which may be a control circuit system.
- the sensor disclosed in FIG. 1a is a galvanic sensor in which there is an electric current in the circuit via resistor 15, between cathode 12 and anode 14. It is adaptable to polarographic operation.
- FIG. 1b The system of FIG. 1b is similar, except it is a dual unit in which a pair of sensing cathodes 18 and 19 utilize a common anode 20.
- Cathode 18 and anode 20 are connected in a circuit with a resistor (or resistance network) 21 to provide one output to its related sensing circuit 22, and a second sensing circuit constituted by cathode 19, anode 20, resistor 23, and sensing circuit 24 which supply the second of dual outputs to a control or display circuit 25.
- a resistor or resistance network
- FIG. 1c The system shown in FIG. 1c is similar to that shown in FIG. 1b in that it is a dual-type system.
- a first half is constituted by a cathode electrode 27, anode electrode 28 connected in circuit across a resistor (or resistance network) 29 which, in turn, is connected to a sensing circuit 30 and a control utilization device constituted by control and display unit 31.
- the second or dual part of the cell is similarly constituted by a cathode electrode 32, anode electrode 33, connected in circuit across a sensing resistor 34 which is coupled to sensing circuit 35 and utilization circuit 31.
- the unit shown in FIG. 1d incorporates a common cathode 39 and a dual anode 40, 41 which are connected, across resistors (or resistance networks) 42 and 43, respectively.
- One of the anodes is made smaller than the other anodes so that presumably, that anode would be consumed at an earlier time than the larger anode and a drop in the signal from that anode, in comparison to the larger anode would provide a signal, or an indication of, the end-of-life of the sensor.
- FIGS. 2a and 2b The present invention is depicted in FIGS. 2a and 2b.
- an electrochemical gas measuring system comprising a gas entry limiting or controlling member 50 which may be a gas diffusion membrane, capillary system or the like, a sensing cathode electrode 52 which may be a conventional gold-plated, perforated disk 52, two or more anode electrodes 53, 54 which are consumable electrodes typically composed of lead or like materials, and an electrolyte 55 (such as potassium hydroxide, for example) housed in a housing H.
- the cathode electrode 52 is connected by an output lead 56 to one end of sensing or load resistor (or resistance network) 57 and as one input to-the sensing circuit 58.
- the anode electrodes 53 and 54 are connected to a switch member 60 which may be an electronic switch so that the anode electrodes 53 and 54 are alternately connected in circuit with the cathode electrode 52 so that the current is always flowing through resistor 57 and the position of switch 60 is conveyed to the sensing and control circuit on line 61.
- the anode electrode is comprised of at least a pair of electrodes 53, 54 which are sequentially and alternately (in FIG. 2a) connected ill a sensing circuit through sensing resistor 57.
- the sensing circuit 58 detects a drop in current from any of the anode electrodes relative to the others of the anodes as an indication of the end of the useful life of the sensor.
- the utilization circuit 62 can operate a control valve CV.
- the control valve CV is an oxygen control valve to the baby's isolette.
- the sensing circuit may include a further circuit for signalling to the user, such as an indicator light IL, that the sensor must be replaced in a short period of time. Meanwhile, the circuit operates on the remaining anode electrode with the user being provided with an indication or warning that the sensor must be replaced in a short period of time.
- the gas entry limiting means can be a gas diffusion membrane, or capillary, or the like.
- the control system or control circuit 62 is preferably programmed or adapted to control the oxygen level based on other than the lower (lowest) of the anode currents e.g., the higher (highest) of the anode currents.
- a gaseous diffusion membrane 50 constitutes the gas entry limiting means.
- the gas entry limiting means can be a capillary-type member 52'.
- the cathode or sensing electrode 52' is common to a plurality of anodes 61-1, 61-2 . . . 61-N with a scanning switch or multiplexer 64 individually connecting the anode electrodes 61-1, 61-2 . . . 61-N in sequence in circuit with sensing resistor 57' and cathode electrode 52'.
- High speed scanning switch or multiplexer 64 like switch 60, may dwell on the individual anodes 61-1, 61-2 . . .
- the switching time between anodes is extremely rapid so that the sensing circuit is essentially always closed and any gas which enters into the sensor does not build-up to any significant extent so as to adversely affect the current readings.
- the multiplexer can be controlled, and is typically a sequential scanning of the anodes 61-1, 61-2 . . . 61-N, it will be appreciated that the sensing circuit can cause the multiplexer 64 to skip those anode electrodes which have been determined by the sensing circuit to be "consumed” or have reached the end of their respective lives, so that only those anode electrodes which have useful life are actually scanned to the end of the useful life of the last of those to be useful.
- the invention is not limited to sensors measuring oxidizing (reducible) gasses (such as O 2 , NO 2 , Cl 2 , etc.) but is also useable with sensors measuring electro-chemically oxidizable gasses such as NO, CO, and H 2 S.
- oxidizing (reducible) gasses such as O 2 , NO 2 , Cl 2 , etc.
- electro-chemically oxidizable gasses such as NO, CO, and H 2 S.
- the anode is the sensing electrode and the cathode may be expended.
- the same arrangement would be used but with multiple (two or more) cathodes and a single anode. With reference to FIG. 2a, in such a case, the anode would correspond to element 52 and tile cathode would correspond to elements 53 and 54.
- the basic cell design parameters for such cells are well known to those skilled in the art.
- a gas entry limiting means is employed.
- sensors which are designed to measure gasses which only constitute a small portion of the gas to which the sensor is exposed for example H 2 S or CO in ambient air
- the flow limiting mechanism may not be needed.
- the components 50 and 52, respectively can be a gas entry means rather than gas entry limiting means.
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Abstract
Description
Claims (12)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US08/264,266 US5405512A (en) | 1994-06-23 | 1994-06-23 | Gas sensor and method |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US08/264,266 US5405512A (en) | 1994-06-23 | 1994-06-23 | Gas sensor and method |
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US5405512A true US5405512A (en) | 1995-04-11 |
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US08/264,266 Expired - Lifetime US5405512A (en) | 1994-06-23 | 1994-06-23 | Gas sensor and method |
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Cited By (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5733436A (en) * | 1995-03-23 | 1998-03-31 | Testo Gmbh & Co. | Method for determining the state of an electrochemical gas sensor |
GB2340612A (en) * | 1998-08-18 | 2000-02-23 | Ind Scient Corp | Determining end of useful life of electrochemical gas sensor with consumable electrode |
US6439138B1 (en) * | 1998-05-29 | 2002-08-27 | Hamon Research-Cottrell, Inc. | Char for contaminant removal in resource recovery unit |
US6558519B1 (en) * | 1996-12-07 | 2003-05-06 | Central Research Laboratories Limited | Gas sensors |
US20090013107A1 (en) * | 2003-09-23 | 2009-01-08 | Detlev Wittmer | Method for Safe Data Transmission Between an Intrinsically Safe Sensor and a Non-Intrinsically Safe Evaluation Unit |
US20120145561A1 (en) * | 2009-07-06 | 2012-06-14 | Veolia Water Solutions & Technologies Support | Device for Measuring at Least One Property of Water |
CN106647508A (en) * | 2016-08-29 | 2017-05-10 | 江苏师范大学 | Photocatalysis application device including air pressure sensing module and photocatalyst application machine |
US11579129B2 (en) | 2019-11-27 | 2023-02-14 | Accutron Instruments Inc. | Method and system for testing and calibrating gas sensors |
Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3849725A (en) * | 1972-09-18 | 1974-11-19 | Asahi Optical Co Ltd | Circuit for switching different resistance values corresponding to amount of light measured |
US4260985A (en) * | 1979-02-14 | 1981-04-07 | Trw Inc. | Resistive device sensor |
US4845435A (en) * | 1988-01-20 | 1989-07-04 | Honeywell Inc. | Sensor fault detector |
US5273640A (en) * | 1990-06-11 | 1993-12-28 | Matsushita Electric Works, Ltd. | Electrochemical gas sensor |
-
1994
- 1994-06-23 US US08/264,266 patent/US5405512A/en not_active Expired - Lifetime
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3849725A (en) * | 1972-09-18 | 1974-11-19 | Asahi Optical Co Ltd | Circuit for switching different resistance values corresponding to amount of light measured |
US4260985A (en) * | 1979-02-14 | 1981-04-07 | Trw Inc. | Resistive device sensor |
US4845435A (en) * | 1988-01-20 | 1989-07-04 | Honeywell Inc. | Sensor fault detector |
US5273640A (en) * | 1990-06-11 | 1993-12-28 | Matsushita Electric Works, Ltd. | Electrochemical gas sensor |
Cited By (10)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5733436A (en) * | 1995-03-23 | 1998-03-31 | Testo Gmbh & Co. | Method for determining the state of an electrochemical gas sensor |
US6558519B1 (en) * | 1996-12-07 | 2003-05-06 | Central Research Laboratories Limited | Gas sensors |
US6439138B1 (en) * | 1998-05-29 | 2002-08-27 | Hamon Research-Cottrell, Inc. | Char for contaminant removal in resource recovery unit |
GB2340612A (en) * | 1998-08-18 | 2000-02-23 | Ind Scient Corp | Determining end of useful life of electrochemical gas sensor with consumable electrode |
GB2340612B (en) * | 1998-08-18 | 2003-02-26 | Ind Scient Corp | Method for determining exhaustion of an electrochemical gas sensor |
US20090013107A1 (en) * | 2003-09-23 | 2009-01-08 | Detlev Wittmer | Method for Safe Data Transmission Between an Intrinsically Safe Sensor and a Non-Intrinsically Safe Evaluation Unit |
US20120145561A1 (en) * | 2009-07-06 | 2012-06-14 | Veolia Water Solutions & Technologies Support | Device for Measuring at Least One Property of Water |
CN106647508A (en) * | 2016-08-29 | 2017-05-10 | 江苏师范大学 | Photocatalysis application device including air pressure sensing module and photocatalyst application machine |
CN106647508B (en) * | 2016-08-29 | 2018-10-30 | 江苏师范大学 | Photocatalysis application device including air pressure sensing module and photocatalyst application machine |
US11579129B2 (en) | 2019-11-27 | 2023-02-14 | Accutron Instruments Inc. | Method and system for testing and calibrating gas sensors |
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